I. Field of the Present Invention
The present invention relates generally to metal making apparatus, and more particularly to apparatus for separating slag from molten metal as the molten metal is transferred from a receptacle.
II. Description of the Prior Art
In metal making processes, such as steel making, a layer of slag comprising metal impurities lies atop the surface of the molten metal held within a receptacle. When the molten metal is drained from the receptacle, it is important to maintain the separation between the slag and molten metal so that the high quality steel being discharged is not contaminated by the slag. For example, in the formation of a continuous, steel strand, a receptacle known as a tundish receives molten metal from numerous ladles for distribution to the strand making mold through a single discharge nozzle. The nozzle is located in the bottom wall of the tundish so that the nozzle is in fluid contact only with the layer of molten metal in the tundish and is separated from the slag at the top surface of the molten metal.
However, in a previously known tundish, the flow of molten metal through the discharge nozzle causes a vortex which introduces a swirl to the molten metal within the tundish above the discharge nozzle. When the tundish is filled to a high level, the minor swirl imparted to the fluid does not affect the separation between the slag layer and the steel layer. However, when the fluid level reaches a certain depth, hereinafter referred to as the critical level, which is dependent upon the size of the discharge nozzle, the vortex forms a funnel which sucks the slag layer down through the center of the vortex and into the discharge nozzle along with the high quality molten metal. At this point, the quality of the strand being formed is substantially affected by contamination of the slag. As a result, it has heretofore been necessary to halt the strand formation and begin the formation of a reduced quality product or permit the metal to harden in the tundish for subsequent remelting when the level of metal can be raised above the critical level.
Unfortunately, the level of fluid at which the vortex suction effect occurs is relatively high, whereby a substantial amount of high quality molten metal remains trapped within the tundish. As a result, substantially less high quality metal is available for strand forming than has actually been produced. Moreover, substantial energy input is required to reheat metal which has hardened within the tundish.
Furthermore, even if the strand forming process is changed in order to form strands of substantially lower quality steel, it has heretofore been difficult to detect or sense when the level of molten metal is at the critical level in the tundish. Since the suction action of the vortex draws the slag into the center of the vortex, a person operating the tundish cannot see that slag is flowing through the nozzle since molten metal surrounds the slag as it passes through the nozzle. Rather, the surfacing of slag in the strand mold has heretofore provided an indication that the critical level has been reached, but such an indication occurs only after contamination of the high quality steel strand.